Establishing a link between climate change and mental health, the World Health Organisation has said extreme weather conditions like floods, droughts and natural calamities can lead to psychiatric illnesses.

"Psychosocial illnesses are a part of the various health issues associated with climate change," Poonam Khetrapal Singh, Deputy Regional Director, WHO, said.

Anticipating that severe flooding may become more frequent due to global warming, a WHO report said that independent studies in cyclone-affected Orissa and a flooded town in England has shown that post-traumatic stress disorder syndromes of different severity in affected people even after an year.

Another area is the mental health impact of drought, a likely sequence of climate change. Drought-affected farmers can undergo severe mental agony due to financial hardship from increased debt, it said.

It is difficult for farmers to plan for crops, stocking, improvements, breeding and succession. This affects other businesses, limiting their ability to expand and employ staff.

Drought affects family relationships also leading to stress, worry and an increase in the rate of suicides. It can also lead to isolation and increased workload as fewer workers take on more work, partners move off the farm for additional income or for school needs and families can no longer afford social support.

"The phenomenon of farmers' suicides in India is a typical example of consequences of climatic vagaries in poor, predominantly agrarian economies," the report said.

The report goes on to say that in general population, the 12-month prevalence rate of mild and moderate common mental disorders is on an average of about 10 per cent in countries across the world.

However, this rate is likely to rise possibly to 20 per cent after exposure to severe trauma and resource loss.

In case of severe mental disorders, like psychosis, the 2-3 per cent rate in general population may be expected to go up (3-4 per cent) after exposure to severe disaster.

Following the Asian tsunami, the WHO estimated that 20-40 per cent of affected people suffered from short-lasting mild psychological distress and another 30-50 per cent experienced moderate-to-severe psychological stress.

The hurricane 'Katrina' in United States has been associated with a high prevalence of psychiatric morbidity. In a survey with a sample of 1043 affected residents, the 30-day prevalence of anxiety-mood disorders was found to be 49.1 per cent and that of PTSD 26.4 per cent, it said.

This shows that people living in poverty, those geographically vulnerable to extreme weather events, those highly dependent on agriculture for livelihood and those vulnerable to develop mental illness are at high risk, the report added.